Oxidation of 5-(hydroxymethyl) furfural to 2,5-diformylfuran and subsequent decarbonylation to unsubstituted furan

ABSTRACT

Alcohols are catalytically oxidized to aldehydes, in particular to benzaldehyde and diformylfuran, which are useful as intermediates for a multiplicity of purposes. The invention also relates to the polymerization of the dialdehyde and to the decarbonylation of the dialdehyde to furan.

FIELD OF INVENTION

The invention relates to the catalytic oxidation of alcohols toaldehydes, in particular the formation of benzaldehyde anddiformylfuran, which are useful as intermediates for a multiplicity ofpurposes. The invention also relates to the polymerization and thedecarbonylation of a dialdehyde.

BACKGROUND

5-(Hydroxymethyl)furfural (HMF) is a versatile intermediate that can beobtained in high yield from biomass sources such as naturally occurringcarbohydrates, including fructose, glucose, sucrose, and starch.Specifically, HMF is a conversion product of hexoses with 6 carbonatoms. It is known that HMF can be oxidized using a variety of reagentsto form any of four different products, which can themselves beconverted to one or more of the others:

The selective oxidation of an alcohol functionality in the presence ofan aldehyde functionality on the same compound is difficult because ofthe high reactivity of the aldehyde group. Furthermore, if HMF isreacted with molecular oxygen (O₂), the aldehyde functionality would beexpected to oxidize more rapidly than the alcohol and the expectedproduct would be predominantly 5-(hydroxymethyl)furan-2-carboxylic acid(Sheldon, R. A. and Kochi, J. K. “Metal Catalyzed Oxidations of OrganicCompounds”, Academic Press, New York, N.Y. 1981, p 19).

Diformylfuran (DFF) has been prepared from HMF using CrO₃ and K₂Cr₂O₇(L. Cottier et al., Org Prep. Proced Int. (1995), 27(5), 564; JP54009260) but these methods are expensive and results in large amountsof inorganic salts as waste. Heterogeneous catalysis using vanadiumcompounds has also been used, but the catalysts have shown low turnovernumbers (DE 19615878, Moreau, C. et al., Stud. Surf Sci. Catal (1997),108, 399-406). Catalytic oxidation has been demonstrated using hydrogenperoxide (M. P. J. Van Deurzen, Carbohydrate Chem. (1997), 16(3), 299)and dinitrogen tetraoxide (JP 55049368) which are expensive. Therelatively inexpensive molecular oxygen (O₂) has been used with a Pt/Ccatalyst (U.S. Pat. No. 4,977,283) to form both DFF andfuran-2,5-dicarboxlic acid (FDA), but yielded low amounts of DFF. Goodyields were found for FDA, but only as the disodium salt which resultedin wasteful salt formation during conversion to the acid form.

Metal bromide catalysts have been used to oxidize substitutedalkylbenzenes to various products including the oxidation of alkyl toaldehydes, alkyl to alcohols, alkyl to acids, alcohol to acid, andaldehydes to acids (W. Partenheimer, Catalysis Today, 23(2), 69-158,(1995)). However, in such cases, the aldehyde product is either a minorcomponent or is quickly oxidized further. FDA has also been preparedusing a Co/Mn/Br catalyst from 5-methyfurfural with DFF seen as a minorbyproduct (V. A. Slavinskaya, et al., React. Kinet. Catal. Lett. (1979),11(3), 215-20).

DFF has been polymerized to form polypinacols and polyvinyls (Cooke, etal., Macromolecules 1991, 24, 1404). However, preparation of polyestersprepared from diformylfuran is not known in the literature.

DFF can also be used to produce unsubstituted furan. Unsubstituted furanis an important commodity in the chemical industry used in theproduction of tetahydrofuran. Supported metal catalysts have been usedin the decarbonylation of the monoaldehyde furfural to furan, but abasic promoter is required, adding expense and complexity to the process(U.S. Pat. No. 3,007,941, U.S. Pat. No. 4,780,552).

Considering the aforementioned discussion, there is a need for aninexpensive, high yield process for the preparation of both DFP and FDAthat does not produce large amounts of waste products and which lendsitself to easy separation and purification. Additionally, there is aneed for a high yielding. process to prepare unsubstituted furan fromrelatively inexpensive, renewable sources.

SUMMARY OF THE INVENTION

The invention is directed to a first process for the preparation of adialdehyde comprising a) contacting a compound containing an alcoholfunctionality and an aldehyde functionality with an oxidant in thepresence of a metal bromide catalyst; and b) optionally isolating thedialdehyde product. A preferred metal bromide catalyst comprises asource of bromine and at least one metal selected from the groupconsisting of Co and Mn, and optionally containing Zr. More preferablythe metal bromide catalyst contains Co.

Preferably the dialdehyde is of the formula H(C═O)—R—(C═O)H and thecompound is of the formula HOH₂C—R—(C═O)H, wherein R is selected fromthe group consisting of an optionally substituted C₁-C₂₀ alkyl or arylgroup. The R groups can be linear or cyclic, or a heterocyclic group.More preferably, R is furan, and most preferably the dialdehyde is2,5-di(formyl)furan. The process of the present invention can be run ina solvent mixture comprising at least one aliphatic C₂-C₆ monocarboxylicacid compound, preferably acetic acid.

The invention is further directed to a second process for thepreparation of a diacid of the formula HOOC—R′—COOH from analcohol/aldehyde of the formula HOH₂C—R′—(C═O)H, wherein R′ is anoptionally substituted furan ring, comprising the steps:

-   -   (a) contacting the alcohol/aldehyde with an oxidant in the        presence of a metal bromide catalyst forming an alcohol/acid        having the formula HOH₂C—R′—COOH, and optionally isolating the        alcohol/acid;    -   (b) contacting the alcohol/acid with an oxidant in the presence        of a metal bromide catalyst forming an acid/aldehyde having the        formula HOOC—R′—(C═O)H, and optionally isolating the        acid/aldehyde;    -   (c) contacting the acid/dialdehyde with an oxidant in the        presence of a metal bromide catalyst forming the diacid,        optionally isolating the diacid.

The invention is further directed to a third process for the preparationof a diacid of the formula HOOC—R′—COOH from an alcohol/aldehyde of theformula HOH₂C—R′—(C═O)H, wherein R′ is an optionally substituted furanring, comprising the steps:

-   -   (a′) contacting the alcohol/aldehyde with an oxidant in the        presence of a metal bromide catalyst forming a dialdehyde having        the formula H(C═O)—R′—(C═O)H, and optionally isolating the        dialdehyde;    -   (b′) contacting the dialdehyde with an oxidant in the presence        of a metal bromide catalyst forming an acid/aldehyde having the        formula HOOC—R′—(C═O)H, and optionally isolating the        acid/aldehyde; and    -   (c′) contacting the acid/dialdehyde with an oxidant in the        presence of a metal bromide catalyst forming the diacid, and        optionally isolating the diacid.

The process further comprises the steps of a′, b′, and c′ and whereinbefore step c′ the acid/aldehyde is converted to an acetate ester of theformula CH₃(C═O)OCH₂—R′—(C═O)H.

Preferably, in the above process the diacid is furan-2,5-dicarboxlicacid and the alcohol/aldehyde is 5-(hydroxymethyl)furfural.

The process can optionally be run in a solvent or solvent mixturecomprising at least one aliphatic C₂-C₆ monocarboxylic acid compound,preferably acetic acid.

The invention is also directed to a fourth process for the preparationof an aldehyde comprising a) contacting a compound of the formulaAR—CH₂—OH wherein AR is an optionally substituted aryl with an oxidantin the presence of a metal bromide catalyst; and b) optionally isolatingthe aldehyde product. Preferably, AR an optionally substituted phenylgroup. Most preferably, AR is an unsubstituted phenyl group. A preferredmetal bromide catalyst is comprised of a source of bromine and at leastone metal selected from the group consisting of Co and Mn. Morepreferably the metal bromide catalyst contains Co.

The process can be run in a solvent or solvent mixture comprising atleast one aliphatic C₂-C₆ monocarboxylic acid compound, preferablyacetic acid.

The invention is also directed to a fifth process to form a polyesterpolymer and the polyester polymer so produced from 2,5-diformylfurancomprising the repeat units A and B and C.

wherein said process comprises polymerization of di(formyl)furan. Theprocess can be performed in the presence of a catalyst of the formulaM^(+n)(O-Q)_(n) wherein M is a metal, n is the positive charge on themetal, and Q is an alkyl group of 1-4 carbons. Preferably, M is aluminumand n is three. Preferably the polyester polymer formed from the processis a homopolymer.

An embodiment of the invention is a polyester polymer comprisingrepeating units A, B and C. Preferably, the polyester polymer is ahomopolymer.

Another aspect of the invention is a sixth process for the preparationof furan comprising converting 2,5-diformylfuran into furan and furfuralvia decarbonylation in the presence of a catalytic amount of a compoundconsisting essentially of a optionally supported metal selected fromPeriodic Group VIII. The furan and furfural product may further beconverted via decarbonylation into unsubstituted furan in the presenceof a catalytic amount of a compound consisting of an optionallysupported metal selected from Periodic Group VIII.

Preferably the catalyst is supported on a catalyst support member, morepreferably the metal is palladium and the catalyst support member iscarbon.

Another aspect of the invention is to convert the dialdehyde preparedusing the above processes, wherein the dialdehyde is2,5-di(formyl)furan, into furan via decarbonylation in the presence of acatalytic amount of a compound consisting of a optionally supportedmetal selected from Periodic Group VIII.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a first process for the preparation of adialdehyde comprising contacting a first compound containing an alcoholfunctionality and an aldehyde functionality with an oxidant in thepresence of a metal bromide catalyst. More specifically, the alcohol canbe HMF, the dialdehyde can be DFF, and the catalyst can be comprised ofCo and/or Mn, and Br, and optionally Zr.

In addition to the alcohol and the aldehyde, other functional groups maybe attached to the first compound as long as the other functional groupsare substantially inert under reaction conditions. In a preferredprocess the first compound is of the formula HOH₂C—R—(C═O)H, and theresulting dialdehyde product that is prepared is of the formulaH(C═O)—R—(C═O)H. In the above formula for the first compound and thedialdehyde product of this invention, R is selected from the groupconsisting of an optionally substituted C₁-C₂₀ alkyl and optionallysubstituted C₁-C₂₀ aryl group. The R groups are either linear, cyclic,or heterocyclic. More preferred is where R is selected from the groupconsisting of an optionally substituted C₁-C₂₀ alkyl group, linear orcyclic, and a heterocyclic group. Most preferred is where R is a furan.By optionally substituted herein is meant a group that may besubstituted and may contain one or more substituent groups that do notcause the compound to be unstable or unsuitable for the use or reactionintended. Substituent groups which are generally useful include nitrile,ether, alkyl, ester, halo, amino (including primary, secondary andtertiary amino), hydroxy, silyl or substituted silyl, nitro, andthioether.

The term “aryl” refers to an aromatic carbo-cyclic group having a singlering (e.g., phenyl), multiple rings (e.g., biphenyl), or multiplecondensed rings of which at least one is aromatic (e.g.,1,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl), andwhich is optionally mono-, di-, or tri-substituted with a functionalgroup such as halogen, lower alkyl, lower alkoxy, lower alkylthio,trifluoromethyl, lower acyloxy, aryl, heteroaryl, and hydroxy. The term“aryl” also refers to heteroaryl groups where heteroaryl is defined as5-, 6-, or 7-membered aromatic ring systems having at least onehetero-atom selected from the group consisting of nitrogen, oxygen andsulfur. Examples of heteroaryl groups are pyridyl, pyrimidinyl,pyrrolyl, pyrazolyl, pyrazinyl, pyridazinyl, oxazolyl, furanyl,quinolinyl, isoquinolinyl, thiazolyl, and thienyl, which can optionallybe substituted with, e.g., halogen, lower alkyl, lower alkoxy, loweralkylthio, trifluoromethyl, lower acyloxy, aryl, heteroaryl, andhydroxy.

A particularly preferred process is where R is 2,5-disubstituted furan,i.e., where the first compound is HMF and the dialdehyde is DFF.

DFF may be further converted via loss of CO to furan, which can behydrogenated to tetrahydrofuran using standard techniques familiar tothose skilled in the art.

The second process concerns preparation of a diacid of the formulaHOOC—R′—COOH from an alcohol/aldehyde of the formula HOH₂C—R′—(C═O)H.

The third process concerns preparation of a diacid of the formulaHOOC—R′—COOH from an alcohol/aldehyde of the formula HOH₂C—R′—(C═O)H.

In the second and third processes, R′ is preferably an optionallysubstituted furan ring. More preferably, R′ is a 2,5-disubstituted furanring. A preferred metal bromide catalyst is comprised of a source ofbromine and at least one metal selected from the group consisting of Coand Mn, and optionally containing Zr. More preferably the metal bromidecatalyst contains Co.

Any of the intermediates, the alcohol/acid, acid/aldehyde, or thedialdehyde, may be isolated at any step, or the reaction may proceedwithout any purification. It is contemplated that the processes of theinvention in which DFF and/or FDA is prepared can be run using a biomassfeedstock containing HMF, such that only the final product need beisolated and purified.

For the preparation of the dialdehyde, the preferred temperatures areabout 20° to 200° C., most preferably about 40° to 130° C. Thecorresponding pressure is such to keep the solvent mostly in the liquidphase. The preferred time of the reaction is determined by thetemperature, pressure, and catalyst concentration such that maximumyield of dialdehyde is obtained. For preparation of diacid, thepreferred temperatures are about 50° to 250° C., most preferentiallyabout 50° to 160° C. The corresponding pressure is such to keep thesolvent mostly in the liquid phase. The preferred time of the reactionis determined by the temperature, pressure and catalyst concentrationsuch that a maximum yield of diacid is obtained.

The fourth process concerns preparation of an aldehyde comprisingcontacting a compound of the formula AR—CH₂—OH, wherein AR is anoptionally substituted aryl group, with an oxidant in the presence of ametal bromide catalyst. Preferably, AR an optionally substituted phenylgroup. Most preferably, AR is an unsubstituted phenyl group. In additionto the alcohol, other functional groups may be attached to the compoundas long as the other functional groups are substantially inert underreaction conditions.

A preferred metal bromide catalyst is comprised of a source of bromineand at least one metal selected from the group consisting of Co and Mn,and optionally containing Zr. More preferably the metal bromide catalystcontains Co.

The process can be run in a solvent or solvent mixture comprising atleast one aliphatic C₂-C₆ monocarboxylic acid compound, preferablyacetic acid.

Metal bromide catalysts employed in all of the processes of thisinvention comprise a soluble transition metal compound and solublebromine-containing compound. One metal or a combination of two or moremetals may be present. Many such combinations are known and may be usedin the processes of the instant invention. These metal bromide catalystsare described further in W. Partenheimer, Catalysis Today, 23(2),69-158, (1995), in particular pages 89-99, herein incorporated byreference. Preferably the metal is cobalt and/or manganese, optionallycontaining zirconium. More preferably, the catalyst is comprised ofCo/Mn/Zr/Br in the molar ratios of 1.0/1.0/0.1/2.0. The amount ofcatalyst in the reaction mixture can be 59/55/203/4 ppm to5900/5500/20000/390 ppm Co/Mn/Zr/Br, preferably 150/140/510/10 ppm to2400/2200/8100/160 ppm (g of metal/g of solvent). As used herein, themolar ratio is the ratio of moles of the metals alone, not the metals asin their compound forms.

Each of the metal components can be provided in any of their known ionicor combined forms. Preferably the metal or metals are in a form that issoluble in the reaction solvent. Examples of suitable forms include, butare not limited to, metal carbonate, metal acetate, metal acetatetetrahydrate, and metal bromide. Preferably metal acetate tetrahydratesare used.

The source of bromide can be any compound that produces bromide ions inthe reaction mixture. These compounds include, but are not limited to,hydrogen bromide, hydrobromic acid, sodium bromide, elemental bromine,benzyl bromide, and tetrabromoethane. Preferred is sodium bromide orhydrobromic acid. As used herein, the amount of bromine means the amountmeasured as Br. Thus, the molar ratio of bromine to total of the metalsused in the catalyst is the moles of Br divided by the sum of the molesof the metal.

As described in Partenheimer, ibid, pages 86-88, suitable solvents foruse in the processes of the present invention, described above, musthave at least one component that contains a monocarboxylic acidfunctional group. The solvent may also function as one of the reagents.The processes may be run in a solvent or solvent mixture that does notcontain an acid group, provided that one of the reagents does containsuch a group. Suitable solvents can also be aromatic acids such asbenzoic acid and derivatives thereof. A preferred solvent is analiphatic C₂-C₆ monocarboxylic acid, such as but not limited to aceticacid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid,trimethylacetic acid, and caproic acid and mixtures thereof. Componentsof said mixtures can include benzene, acetonitrile, heptane, aceticanhydride, chlorobenzene, o-dichlorobenzene, and water. Most preferredas solvent is acetic acid. One advantage of using a solvent such asacetic acid is that furan-2,5-dicarboxylic acid is insoluble,facilitating purification of the insoluble product.

The oxidant in the processes of the present invention is preferably anoxygen-containing gas or gas mixture, such as, but not limited to air.Oxygen by itself is also a preferred oxidant.

The processes of the instant invention described above can be conductedin the batch, semi-continuous or continuous mode. Especially for themanufacture of FDA, operation in the batch mode with increasingtemperature at specific times, increasing pressure at specific times,variation of the catalyst concentration at the beginning of thereaction, and variation of the catalyst composition during the reactionis desirable. For example, variation of the catalyst composition duringreaction can be accomplished by addition of cobalt and/or manganeseand/or zirconium, and/or bromide at specified times.

The fifth process concerns the polymerization of di(formyl)furan to forma novel polyester polymer comprising the repeat units A, B and C, asshown in the summary above. The catalysts employed in the polymerizationof di(formyl)furan can be selected from any catalyst used for theesterification of a dialdehyde or two separate aldehydes. Thisesterification is commonly known as the “Tishchenko reaction”. A partiallist of catalysts used for this reaction are those listed inMascarenhas, et al., Org. Letters, 1999, Vol. 1, 9, pg. 1427; U.S. Pat.No. 3,852,335; and Reagents for Organic Synthesis, Fieser (ed.), 1969,Vol. 5, pg. 48, and are herein incorporated by reference. An alternatecatalyst is the Shvo catalyst, [(Ph₄C₅OHOC₅Ph₄)Ru₂(CO)₄(μ-H)], asdescribed in Menashe, et al., Organometallics 1991, 10, 3885. Thisdiscussion concerning the Shvo catalyst is also incorporated herein byreference. Preferred catalysts are metal alkoxides of the formulaM^(+n)(O-Q)_(n) where M is a metal, n is the positive charge on themetal, and Q is an alkyl group of 1-4 carbons. Most preferred is where Mis aluminum and n is three. The catalysts of the invention can beobtained already prepared from manufacturers, or they can be preparedfrom suitable starting materials using methods known in the art.

The repeat units A, B, and C can all be present in the polyester polymerproduct but are present in varying ratios, in any order in which anester linkage is present and a polyester is formed. The term polymer isherein defined to include oligomers of 3 or more repeating units as wellas higher polymers. This polymer would be useful as a molding resin ormay be spun into a fiber.

The polyester polymer produced by the present process may include otherrepeat units in addition to those shown above. Other polyesters havingthe above repeat units include, but are not limited to, polyesteramides,polyesterimides, and polyesterethers. A preferred version of the polymeris a homopolymer.

A preferred embodiment of the present invention is the catalyticdecarbonylation of DFF to form a mixture of unsubstituted furan andfurfural.

in the presence of a catalytic amount of a metal selected from PeriodicGroup VIII, herein defined as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, and Pt.Preferably, the catalyst consists essentially of one or more of thePeriodic Group VIII metals. A particularly preferred catalyst consistsessentially of Pd.

The metals may be in any form including Raney catalysts as known tothose skilled in the art. The catalysts are preferably supported on acatalyst solid support. The catalyst solid support, which includes butnot limited to SiO₂, Al₂O_(3,) carbon, MgO, zirconia, or TiO₂, can beamorphous or crystalline, or a mixture of amorphous and crystallineforms. Selection of an optimal average particle size for the catalystsupports will depend upon such process parameters as reactor residencetime and desired reactor flow rates. The amount of metal on the supportis preferably about 0.5-10% and most preferably 1-5%. The catalysts ofthe invention can be obtained already prepared from manufacturers, orthey can be prepared from suitable starting materials using methodsknown in the art. One typical procedure is by impregnation of thesupport by incipient wetness using a soluble metal salt precursor, suchas the chloride, acetate, nitrate salt, following by reduction underhydrogen gas.

A preferred embodiment of the fifth process is a liquid phase reactionin which the DFF is dissolved in a suitable, inert solvent. Thecatalysts are placed in the solvent in a pressure vessel, and pressuredto about 200-1000 psi, (1.4-6.9 MPa), more preferably about 500 psi (3.4MPa) with an inert gas, preferably nitrogen. The reaction temperature isabout 150° C.-250° C., more preferably about 200° C. The reactionproduct containing furan and furfural can be recycled through theprocess one or more times, to eventually form a reaction productconsisting essentially of furan.

The above process can also be combined with the process to prepare DFFdescribed above, to create a single integrated process wherein DFF isprepared using the metal bromide catalysts described above, thendecarbonylated to furan or furfural.

Materials and Methods

HMF was obtained from Lancaster Synthesis, Windham, N.H. Unlessotherwise stated, all materials were used as received without furtherpurification. All percentages are by mole percent unless otherwisespecified.

EXAMPLES 1-6 Reaction of HMF to DFF at Ambient Air Pressure

In a cylindrical glass fitted with a stirrer and baffles, 0.165 g ofcobalt(II) acetate tetrahydrate, 0.169 g of manganese(H) acetatetetrahydrate, 0.142 g of sodium bromide, 0.220 g biphenyl (GC internalstandard), and 10.02 g of 5-hydroxymethyl(furfural) were admixed with100 g of acetic. The solution was purged with nitrogen gas and thetemperature raised to 75° C. using an external oil bath. The nitrogenwas replaced with air at a flow rate of 100 ml/min at ambientatmospheric pressure. The vent oxygen was constantly monitored andoccasionally liquid and vent gas samples for GC analysis were taken atthe times shown in Table 2. After 30 hrs the reaction was terminated.The results from the liquid samples taken from the reactor duringreaction of Example 1 are given in Table 1. The DFF yield increased withtime to a maximum yield of 51% and then decreases thereafter. Themini-reactor data is summarized in Table 3. The rate of reaction, asgiven by the rate of disappearance of HMF, was dependent upon theconcentration of the catalyst, see especially Examples 3, 4. The maximumyields and chemical species selectivities were also dependent on theconcentration of the catalyst, see Examples 1, 3-6. The dependence ofthe selectivity on the concentration of catalyst is given in detail forExamples 3, 4, and 6 in Table 2. The formation of carbon dioxide andcarbon monoxide are undesirable because they are caused by thedecomposition of HMF and its products, as well as from the solvent,acetic acid. As can be seen in Table 2, increasing the catalystconcentration greatly decreases the, formation of these carbon oxides.Example 4 combines the best yield, shortest reaction time, and one ofthe lowest rates of carbon oxide formation.

2,5-Diformylfuran was isolated from the reaction mass as follows. Theliquid from the reaction mixture was allowed to evaporate. The residueafter evaporation of the reaction mixture was (a) sublimed under vacuum,followed by recrystallization of the sublimate from toluene orcyclohexane; or (b) mixed with silica gel and extracted with hexanes orcyclohexane in a Soxhlet extractor; or (c) extracted with hot toluene,with subsequent filtration of the hot toluene solution through silica,evaporation of the filtrate, and recrystallization of the product fromtoluene or cyclohexane.

One specific example of isolation of DFF is as follows. The darkreaction mixture that was obtained from Example 5, was evaporated todryness on a vacuum line. The resulting waxy green-tan material wastransferred to a sublimation apparatus and sublimed under vacuum (10-50millitorr) at 90° C. (oil bath) to produce 5.2 g (51 mol % based oninitial HMF used) of DFF. The resulting DFF (95% pure; ¹H NMR and GC-MSanalysis) contained 3-5% of 5-acetoxymethylfurfural. DFF that was pureto the limits of spectroscopic detection was obtained byrecrystallization of the sublimate from cyclohexane or toluene/hexanes.¹H NMR (CDCl₃, 25° C.), ppm: 7.4 (s; 2H; furane CH), 9.8 (s; 2H; CHO).¹³C NMR (CD₂Cl₂, 25° C.), ppm: 120.4 (s; CH), 154.8 (s; q C), 179.7 (s,CHO). m/z=124. Alternatively, crude DFF can be purified by filtration ofits concentrated dichloromethane solution through a short silica plug,followed by precipitation from the filtrate with hexanes.

TABLE 1 Formation of Diformylfuran in Example 1 Time, min Conversion, %Selectivity, % Yield, molar, % 66 31.9 44.5 14.2 96 40.3 52.6 21.2 11146.6 54.9 25.6 130 54.7 51.2 28.0 144 54.5 59.4 32.4 171 62.5 55.4 34.6190 66.9 55.5 37.1 204 71.0 52.7 37.4 310 82.9 56.6 46.9 384 88.3 56.149.5 450 92.1 55.5 51.1 516 95.2 53.3 50.7 1368 100 35.1 35.1 1410 10035.7 35.7 1728 100 19.8 19.8 1800 100 19.5 19.5

TABLE 2 Summary of Mini-reactor Oxygenations of Hydroxymethyl(furfural)Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 Temp, ° C. 75 50 then 95⁽⁵⁾ 75 75 50 then75⁽⁶⁾ 75 HMF, g 10.015 9.143 10.139 10.051 10.04 10.158 HOAc,g 100 100100 100 100 100.1 Ca, M 0.066 0.026 0.066 0.135 0.268 0273 Mn, M 0.0690.025 0.069 0.139 0.274 0.278 Br, M 0.137 0.050 0.137 0.279 0.557 0.580Zr, M 0.005 0.000 0.005 0.005 0.005 0.005 HMF rate, s⁻¹⁽¹⁾ 9.68E⁻⁰⁵9.28E⁻⁰⁵ 8.13E⁻⁰⁵ 1.64E⁻⁰⁴ — 1.37E⁻⁰⁴ HMF half-life 119 124 142 70 — 84R2 0.998 0.878 0.972 0.999 — 0.994 DFFY,max⁽²⁾ 51 41 50 57 51 52Time,max 450 414 642 310 550 430 C,max 92 98 95 91 95 97 S,max 55 42 5363 54 54 time,min⁽³⁾ 1800 564 640 366 550 430 C, % 100 99 95 95 95 97 S,% 19 41 53 58 54 54 Y, % 19 40 50 55 51 52 HMF acet, % 0.4 8.4 7.5 6.14.5 5.7 CO_(x), ml 878 — 1022 257 219 318 HMF to CO_(x) ⁽⁴⁾ 7.4 — 8.52.1 1.8 2.6 Footnotes ⁽¹⁾Determined by rate of disappearance ofhydroxymethyl(furfural). ⁽²⁾Abbreviations used: C = % conversion, S = %selectivity, Y = % molar yield, as determined by GC. Max is the highestobserved during experiment. ⁽³⁾Time when experiment was terminated⁽⁴⁾Loss of HMF due to carbon monoxide and carbon dioxide formation.Assumes no CO_(x) formation from the solvent. ⁽⁵⁾Reaction performed at50° C. for 105 min, then 95° C. for 459 min. Additional Co/Mn/Brcatalyst was add at 115 and 210 min ⁽⁶⁾Reaction performed at 50° C. for180 min, then 75° C. for 370 min

EXAMPLES 7-15 Reaction of HMF to DFF

Table 3 further illustrates that placing HMF with acetic acid andcatalyst metals and then subjecting them to 1000 psi air pressure (7MPa), can produce high yields of DFF. Molar yields up to 63% wereobtained. The yield varied with temperature and type of catalyst used.

TABLE 3 Initial Conditions for the Oxidation of HMF in Shaker Tubes HMF,HMF, DFF yld, Ex. Catalyst HMF, g Co, ppm Mn, ppm HBr, ppm Zr, ppm Temp,° C. Time, hr conv., % select. % % 7 Co/Mn/Br/Zr 0.2504 203 189 551 2050 2 60.4 66.6 40.2 8 Co/Mn/Br/Zr 0.2481 406 378 1102 20 50 2 69.2 65.345.2 9 CofMn/Br 0.2519 203 189 551 0 50 2 60.6 38.4 23.3 10 Co/Mn/Br0.252 406 378 1102 0 50 2 61.7 54.6 33.7 11 Co 0.2516 7000 0 0 0 50 248.3 22.8 11.0 12 Co/Mn/Br/Zr 0.25 203 189 551 20 75 2 82.5 73.2 60.4 13Co/Mn/Br/Zr 0.2517 406 378 1102 20 75 2 99.7 61.6 61.4 14 Co/Mn/Br0.2529 203 189 551 0 75 2 71 54.3 38.6 15 Co/Mn/Br 0.2514 406 378 1102 075 2 92.2 68.3 63.0

EXAMPLES 16-40 The Reaction of HMF to CFF and FDA

Placing HMF in reactors with acetic acid and catalyst metals and havingthem react with air at 1000 psi (7 MPa) gave good yields of FDA. Aparticular advantage of this method is that the majority of FDAprecipitates from solution upon cooling to room temperature. The yieldsto CFF and FDA, reported on Table 4, are those which were obtained fromthe solids only. Table 4 illustrates that different catalysts such asthose using cobalt, or a mixture such as Co/Mn/Br and Co/Mn/Zr/Br allproduced good yields of FDA. It also illustrates that increasingcatalyst concentrations at a given temperature and time, nearly alwaysincreased the FDA yield.

Examples 35 through 37 are to be compared to Examples 38 through 40. Inthe latter series the temperature was staged-initially it was held at75° C. for 2 hrs and then raised to 150° C. for two hrs. This staging ofthe temperature gave higher yields.

TABLE 4 Reaction of HMF to CFF and FDA All reactions at 1000 psi air (7MPa) HMF, Co, Mn, HBr, Zr, Temp, Time, CFF, FDA, Ex. Catalyst g ppm ppmPpm ppm C. hr yld yld 16 Co/Mn/Br/Zr 0.2517 203 189 551 20 100 2 3.118.7 17 Co/Mn/Br/Zr 0.2533 406 378 1102 20 100 2 6.8 42.3 18 Co/Mn/Br0.2522 203 189 551 0 100 2 4.1 29.7 19 Co/Mn/Br 0.2505 406 378 1102 0100 2 3.3 44.8 20 Co 0.2589 7000 0 0 0 100 2 5.1 31.0 21 Co/Mn/Br/Zr0.2483 203 189 551 20 125 2 2.1 36.5 22 Co/Mn/Br/Zr 0.249 406 378 110220 125 2 2.3 45.6 23 Co/Mn/Br 0.2503 203 189 551 0 125 2 1.8 35.2 24Co/Mn/Br 0.2526 406 378 1102 0 125 2 2.2 44.7 25 Co 0.2616 7000 0 0 0125 2 4.3 16.8 26 Co/Mn/Br/Zr 0.7535 406 378 1102 20 105 12 3.1 26.4 27Co/Mn/Br/Zr 0.7568 812 756 2204 20 105 12 4.2 50.6 28 Co/Mn/Br/Zr 0.74981218 1134 3306 20 105 12 2.5 S8.8 29 Co/Mn/Br/Zr 0.5057 406 378 1102 20105 12 2.4 24.1 30 Co/Mn/Br/Zr 0.501 812 756 2204 20 105 12 5.1 44.0 31Co/Mn/Br/Zr 0.4994 1218 1134 3306 20 105 12 5.6 47.4 32 Co/Mn/Br/Zr0.499 406 378 1102 20 105 8 3.3 32.9 33 Co/Mn/Br/Zr 0.5046 812 756 220420 105 8 4.8 41.0 34 Co/Mn/Br/Zr 0.5 1218 1134 3306 20 105 8 7.3 50.6 35Co/Mn/Br/Zr 0.2498 406 378 1102 20 105 2 3.7 36.9 36 Co/Mn/Br/Zr 0.254812 756 2204 20 105 2 4.8 40.9 37 Co/Mn/Br/Zr 0.4988 406 378 1102 20 1052 1.7 14.0 38 Co/Mn/Br/Zr 0.2517 406 378 1102 20 75,150 2,2 5.2 51.4 39Co/Mn/Br/Zr 0.5077 812 756 2204 20 75,150 2,2 6.2 52.9 40 Co/Mn/Br/Zr0.5105 406 378 1102 20 75,150 2,2 6.5 54.6

EXAMPLES 41-59 Oxidation of Benzyl Alcohol

0.247 g of cobalt(II) acetate tetrahydrate, 0.242 g of manganese(II)acetate tetrahydrate, 0.337 g of hydrogen bromide, 0.198 g biphenyl (GCinternal standard), and 9.72 g of benzyl alcohol were placed in 95 g ofacetic acid and 5% water in a cylindrical glass flask fitted with astirrer and baffles. The solution was purged with nitrogen gas and thetemperature raised to 95° C. using an external oil bath. The nitrogenwas replaced with air at a flow rate of 100 ml/min at ambientatmospheric pressure. Samples were withdrawn from the reactor andanalyzed giving the results in Table 5. A yield of 55 mol percentbenzaldehyde is observed. (Values of benzaldehyde, benzyl acetate,benzoic acid in mol % based on benzyl alcohol charged).

TABLE 5 Oxidation of Benzyl Alcohol Benzyl Benzoic Benzaldehyde,acetate, acid, Ex. Time, hr. Conv., % mol % mol % mol % 41 0 10.4 0.3610.9 0 42 0.1 15 1.8 11.3 0 43 0.2 21 5.5 12.9 0 44 0.33 28 10.4 15.1 045 0.5 35 15 16.8 0 46 0.6 41 19.2 18.2 0 47 0.67 44 21.1 18.9 0.27 480.75 48 24.3 19.6 0.35 49 0.87 52 27.3 20.4 0.45 50 1 57 31.5 21.5 0.6151 1.17 62 34.1 22 0.8 52 1.3 67 37.8 22.8 1.02 53 1.4 69 39.7 23.1 1.2154 1.53 73 42 23.5 1.55 55 1.75 78 45.4 24.1 1.75 56 1.92 81 47.6 24.32.45 57 2.1 83 49.3 24.5 2.69 58 2.33 88 52.4 24.6 3.43 59 2.83 93 54.624.2 6.23

EXAMPLE 60 Polymerization of DFF of 5-(hydroxymethyl)-furan-2-carboxylicacid (‘Tishchenko polymerization’)

The reaction was conducted under rigorously dry conditions. The productswere isolated in air. To a mixture of DFF (0.265 g) and dry toluene (6mL) was added aluminum isopropoxide (Aldrich; 45 mg), and the reactionmixture was vigorously stirred at 95° C. (oil bath) for 3 hours. Thegreenish-brown precipitate was filtered off, washed with toluene, anddried under vacuum to give 0.190 g of a tan powder that appeared to beamorphous (fraction A). The combined mother liquor and the washings wereevaporated and dried under vacuum to yield 0.105 g of fraction B as aviscous yellowish oil. ¹H NMR spectra of both fractions A and B(CDCl₃,25° C.) revealed a number of singlets at 5.2-5.4 ppm (—CH₂—O(O)C—),indicative of polyester formation. A sample of the solid product (0.7460mg) was studied by TGA in the temperature range of 40-600° C. The onsetof decomposition was observed around 100-120° C. The total weight lossmeasured was about 10% at 147° C., and about 34% at 294° C.

EXAMPLE 61

The reaction was carried out under nitrogen. The Shvo catalyst([(Ph₄C₅OHOC₅Ph₄)Ru₂(CO)₄(μ-H)]; as described in Menashe, N.; Shvo, Y.Organometallics 1991, 10, 3885; 5 mg) was added to a mixture of DFF (200mg), toluene (5 mL), and formic acid (cocatalyst; 5 μL). The clearsolution was stirred at 100° C. (oil bath) for 3 hours. ¹H NMR analysisof the reaction mixture indicated 50% conversion to polymeric material.More Shvo catalyst (3 mg) was added and the mixture was stirred at 100°C. (oil bath) for 2 days, 90% conversion was reached (¹H NMR).

EXAMPLES 62-69

The catalysts were prepared by taking a carbon support (Englehard Corp.,12 Thompson Rd., E. Windsor, Conn.) and impregnating by incipientwetness a metal salt. The precursors used were NiCl₂.6H₂O (Alfa), Re₂O₇(Alfa), PdCl₂ (Alfa), RuCl₃.×H₂O (Aldrich), H₂PtCl₆ (Johnson Matthey),CrCl₃.6H₂O (Baker), and 5% Rh using RhCl₃.=H₂O(Alfa). The samples weredried and reduced at 400° C. in H₂ for 2 hours. The decarbonylationreactions were performed by dissolving 50 mg of DFF in 1 ml of dioxane,and which was then placed with 50 mg of catalyst in a 5 ml pressurevessel. The vessel was charged to 500 psi with N₂ and heated to 200° C.for 2 hours. The sample was then cooled, vented and the product analyzedby GC-MS Results are shown in Table 6 below.

TABLE 6 Decarbonylation of DFF Selectivity (%) Ex. Catalyst Conv. (%)Furan THF Furfural Others 62 5% Re/carbon 15.6 2.8 0.0 2.1 95.1 63 5%Pt/carbon 46.1 2.2 0.0 42.7 55.0 64 5% Cr/carbon 27.3 1.3 0.0 0.0 98.765 5% Rh/carbon 33.8 1.7 0.0 29.7 68.6 66 5% Ni/carbon 10.3 5.1 0.0 1.793.2 67 5% Pd/carbon 98.6 49.8 1.0 48.1 1.1 68 5% Ru/carbon 25.0 3.5 0.062.9 33.6

1. A process for the preparation of a dialdehyde comprising: contactinga compound containing an alcohol functionality and an aldehydefunctionality with an oxidant in the presence of a metal bromidecatalyst under conditions promoting formation of dialdehyde product toform a reaction mixture.
 2. The process of claim 1 wherein the metalbromide catalyst is comprised of a source of bromine and at least onemetal selected from the group consisting of Co and Mn.
 3. The process ofclaim 1 wherein the metal bromide catalyst comprises Co and Mn.
 4. Theprocess of claim 3 further comprising Zr.
 5. The process of claim 3wherein the oxidant is selected from the group consisting of air andoxygen.
 6. The process of claim 3 wherein the process is run in asolvent or solvent mixture comprised of at least one aliphatic C₂-C₆monocarboxylic acid compound.
 7. The process of claim 6 wherein theprocess is run in acetic acid.
 8. The process of claim 1 wherein thedialdehyde is of the formula H(C═O)—R—(C═O)H and the compound is of theformula HOH₂C—R—(C═O)H, wherein R is selected from the group consistingof a heterocyclic group and a C₁-C₂₀ linear or cyclic optionallysubstituted alkyl or aryl group.
 9. The process of claim 8 wherein R isan optionally substituted furan ring.
 10. The process of claim 8 whereinthe dialdehyde is 2,5-di(formyl)furan.
 11. The process according toclaim 8 further comprising converting the dialdehyde into a furan andfurfural product mix via decarbonylation in the presence of a catalyticamount of an compound consisting of a optionally supported metalselected from Periodic Group VIII.
 12. The process of claim 11 whereinthe process further comprises converting the furan and furfural productmix via decarbonylation into furan in the presence of a catalytic amountof an compound consisting of a optionally supported metal selected fromPeriodic Group VIII.
 13. The process of claim 11 wherein the catalyst issupported on a catalyst support member.
 14. The process according toclaim 13 wherein the metal is palladium and the catalyst support memberis carbon.